Chilling new details have emerged about the two-year-old found dead in her Sydney home.

A young Sydney mother has been charged with murder after her two-year-old daughter was left dead in a bathtub for up to three days, police allege.

The 27-year-old woman appeared in Penrith Local Court by video link on Wednesday morning after she was arrested and charged by police the night before, the Daily Mail reports. She did not apply for bail and was formally refused it.

Detectives believe the toddler was killed at her commission housing residence in the south-western suburb of Miller sometime between 6am on Saturday and 12.30pm on Tuesday.

Police were called about noon on Tuesday after a family friend found the girl’s body covered by a towel lying in the bathtub, according to 9News.

It is understood the family friend had been trying to reach the mother for several days and visited her home after becoming concerned.

Neighbours have been speaking to the media about what they knew of the girl and her mother.

Local Pat Ingram told 9News a family friend approached her about the child.

“Someone knocked on our door, asked if we had seen the little girl. She said she was concerned for the child’s welfare,” Ms Ingram said.

“She asked if I had a ladder, I told her if she was really concerned, she should ring the police.”

The Daily Mail was told the mother was often seen sitting outside her home smoking, but otherwise seemed to be a very private person.

The girl was described as “always happy”.

Neighbour Shannon Francisco told reporters she had “little dark curly hair, she was just gorgeous,” according to 9News. He added he had never been aware of any problems.

“That’s why it’s a big surprise for me,” Francisco said.

It was understood the family had only been in the home for about a year.

Investigators remained at the crime scene late into the night combing for evidence.

A post-mortem examination will determine how the girl died.

The mother will appear in court again later this year.